Snowmobile with a turbocharged four-stroke engine

ABSTRACT

A snowmobile is provided that includes a frame, an engine, an endless belt drive system, and an air intake system for the engine. The frame has a forward portion and an aft portion. The engine is mounted to the forward portion and the belt drive system is mounted to the aft portion and is operatively connected to the engine. The engine is a turbocharged four-stroke type engine.

This application claims priority to U.S application Ser. No. 60/247,052,filed Nov. 13, 2000.

FIELD OF THE INVENTION

The present invention relates, generally to snowmobiles, and moreparticularly, to a snowmobile with a turbocharged four-stroke engine.

BACKGROUND OF THE INVENTION

Snowmobiles have traditionally used two-stroke type engines for powergeneration. Two-stroke type engines generally provide relatively highpower-to-weight and power-to-size ratios, which are extremely desirablecharacteristics in an engine for a snowmobile. Other highly desirablecharacteristics of two-stroke engines in regards to snowmobiles includethe relative simplicity of these types of engines and the relative easeof integration with systems, aided by the relatively highpower-to-weight and power-to-size ratios of these engines.

However, recently there has been a trend to decrease exhaust emissionsfrom internal combustion engines, especially two-stroke engines, due toenvironmental concerns and an increase in regulations related thereto.Generally, two-stroke engines inherently have higher exhaust emissionsthan their four-stroke counterparts due to: 1) the necessity of openingthe exhaust ports subsequent to complete ignition of the fuel/airmixture, 2) unburned fuel escaping the exhaust port during the intakecharging of the cylinder, and 3) lubrication oil mixing with the intakecharge.

Lower emissions-producing four-stroke engines have generally not beenused with snowmobiles due to the relatively lower power-to-weight/sizeratios of these types of engines. Snowmobile performance is extremelysensitive to increases in weight and the relative compact chassis andbody of a snowmobile limits the space available for the engine.Additionally, four-stroke engines can be relatively more difficult tointegrate into vehicles, such as a snowmobile, due to the engine'srelative complexity.

It is known outside the art of snowmobiles to use a turbocharger inconjunction with a four-stroke engine to increase the power output andfuel efficiency of the engine. However, a turbocharged V-twin engine hasnot previously been considered feasible for utilization with asnowmobile.

SUMMARY OF THE INVENTION

The present invention avoids these limitations in the prior art byproviding a snowmobile comprising a frame, an engine, an endless beltdrive system and an air intake system for enhancing performance of theengine. The frame of the snowmobile has a forward portion, with theengine mounted thereto, and an aft portion. The belt drive system ismounted to the aft portion of the frame and is operatively connected tothe engine.

The engine is a four-stroke type with at least one cylinder arranged inan inline or V-twin configuration. Each cylinder includes a respectivecombustion chamber and the engine has an air inlet and an exhaust outletcommunicating with each of the combustion chambers.

The snowmobile of the present invention further comprises an air intakesystem including an air box communicating with the atmosphere. The airbox is a substantially hollow enclosed structure. A turbocharger isconnected to the air box such that air from the air box may enter theturbocharger. The turbocharger communicates with the exhaust outlet andis constructed and arranged such that a flow of exhaust gases from theexhaust outlet through the turbocharger affects a pressurization of airtherein. The pressurization of the air within the turbochargerrelatively increases the temperature of the air therein. Thepressurization amplitude of the air pressurized within the turbochargeris cyclical in amplitude with respect to a cyclical flow of exhaustgases thereto from the exhaust outlet. A heat exchanger formed of a heatconductive material is connected to the turbocharger such that thepressurized air from the turbocharger may enter therein. The heatexchanger is constructed and arranged such that heat from thepressurized air is dissipated therefrom to the atmosphere via the heatconductive material. A plenum is connected to the heat exchanger suchthat air from the heat exchanger may enter the plenum. The plenum isalso connected to the air inlet and is constructed and arranged suchthat the cyclically pressurized amplitude of the air from theturbocharger via the heat exchanger may collect therein such that thepressurization amplitude of the air upon exiting the plenum and enteringthe air inlet is moderated.

Other aspects, features and advantages of the present invention willbecome apparent from the following detailed description, theaccompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a snowmobile embodying the principles ofthe present invention;

FIG. 2 is a schematic view of the air intake system of the presentinvention showing relative gas pressures with bold lines;

FIG. 3 is a schematic view of one embodiment of the engine and airintake system of the present invention;

FIG. 4 is a bottom plan view of an upper portion of the snowmobile shownin FIG. 1;

FIG. 5 is a sectional view of a fastening device;

FIG. 6 is an exploded view of one type of turbocharger;

FIG. 7 is a front plan view of the forward portion of the snowmobileshown in FIG. 1;

FIG. 8 is a front elevational view of the heat exchanger showingpathways of air flow therethrough in phantom;

FIG. 9 is a side view of the heat exchanger in a horizontal arrangementshowing air entrainment;

FIG. 10 is a side view of the heat exchanger in an angled arrangementshowing air entrainment;

FIG. 11 is a schematic view of a V-twin engine and exhaust conduitconnected thereto;

FIG. 12 is a schematic view of a two cylinder, in-line engine equippedwith an air intake system and turbocharger according to the principlesof the present invention;

FIG. 13 is a schematic view of a three cylinder, in-line engine equippedwith an air intake system and turbocharger according to the principlesof the present invention;

FIG. 14 is a schematic view of a V-twin engine, two cylinder in-lineengine, and a three cylinder in-line engine with relative dimensionsindicated; and

FIGS. 15 and 16 are schematic views of an engine with a CVT in differentarrangements.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a snowmobile 10 embodying the principles of the presentinvention. As shown, snowmobile 10 has a tunnel or frame 12, a steeringassembly 14 and an endless belt drive system 16 mounted to an aft endportion of the frame 12. Snowmobile 10 utilizes an internal combustionengine indicated at 100 to provide power generation thereto. Engine 100is operatively connected to the belt drive system 16 to provide movementof the snowmobile 10. The snowmobile 10 additionally includes a seat 18whereon a driver and rider may be positioned in a seated manner thereon.A steering control assembly 20 is located forward of the seat 18 and isoperatively coupled to steering assembly 14 so as to provide a steeringcapability to snowmobile 10.

It is preferable for the engine 100 of the present invention to be afour-stroke type internal combustion engine. Advantages of this type ofengine, as will be described herein below, include lower hydrocarbonemissions. However, several characteristics of four-stroke engines havepreviously rendered this type of engine unfeasible for use in asnowmobile. As such, the present invention is also directed toward anair intake system for the snowmobile 10 with a four-stroke engine.

An air intake system of the present invention is shown schematically inFIG. 2 at 22. As shown in FIG. 2, air from the atmosphere enters an airbox or passage 200 at A, flows therethrough and enters a turbocharger300 at B. Within the turbocharger 300, the air is pressurized, as wellas heated due to the rapid pressurization and heat conduction from theengine's exhaust such that at an exit point C the temperature andpressure of the air exiting the turbocharger 300 are greater than apressure and temperature of the air entering the turbocharger at B. Theheated and pressurized air then flows to an entrance D of a heatexchanger 400 (commonly referred to as an intercooler). The heatexchanger 400 is constructed and arranged to remove heat from thepressurized air such that at an exit point E, the temperature of the airis less than the temperature of the air at the entrance point D. As willbe described below in more detail, the turbocharger 300 additionallyadds a pulsed amplitude signature to the air being pressurized (andheated) therein. Upon exit from the heat exchanger at E, the air thenflows to an entrance F of a plenum 500. The plenum 500, as will bedescribed below, forms a voluminous enclosure that significantly reducesthe pulsed signature from the amplitude of the pressurized air. Thepressurized air then exits the plenum at G and enters the internalcombustion engine at H. Further shown in FIG. 2, exhaust gases exit theinternal combustion engine 100 at I and enter the turbocharger 300 at J.As will be described below, the exhaust gases entering the turbocharger300 affect the compression of the air entering the turbocharger 300 atB, as well as introduce the pulsed nature of the pressurized air exitingthe turbocharger at C. The exhaust gases then exit the turbocharger 300at K and exit the snowmobile through an exhaust system 24 describedbelow.

FIG. 3 shows an exemplary arrangement of the air intake system 22 shownin FIG. 2. As shown, air box 200 is situated proximate a forward end 26of snowmobile 10 and is mounted to a forward portion thereof. The airbox 200 is shown relatively forward of engine 100 and adjacent thereto.In the illustrated embodiment shown in FIG. 3, the turbocharger 300 ispositioned on a starboard side of the engine 100 and adjacent thereto.Shown in FIG. 3, the heat exchanger 400 is positioned at the forward end26 beneath the air box 200. The plenum 500 is located on a port side ofthe engine 100 and is operatively connected thereto.

As shown in FIG. 3, air box 200 is essentially a hollow voluminousstructure. The air box 200 includes an inlet 202, which communicateswith the atmosphere surrounding the snowmobile 10. It is preferable forthe air box 200 to include one or more interior walls 204 that dividethe interior periphery of the air box 200 into two or more chambers.FIG. 3 shows two such chambers, indicated at 205A and 205B. It ispreferable for the chambers 205A and 205B to be interconnected by one ormore baffles 206 such that air may flow through the inlet 202 throughthe baffle 206 and exit the air box 200 from an outlet 208. The baffle206, as illustrated, may be in the form of a tubular member protrudingthrough the interior wall 204 providing an air path 207 therethrough. Itis noted that the baffle 206 may also be in the form of an openingwithin the interior wall 204 providing the air path 207 therethrough. Itis contemplated that each chamber of the air box 200 may communicatewith adjacent chambers by one or more baffles 206. It is noted that thebaffles 206 are preferable to reduce intake roar from the engine. Thebaffles 206 should be configured so as to minimize flow resistance ofthe air traveling therethrough. It is contemplated that by increasingthe breadth of the air path 207 within each baffle, flow resistance maybe reduced. It is further contemplated that a flared portion 209 may beformed on the incoming air side of each baffle to reduce flow resistanceof air through the baffles. A duct member or conduit 210 extends fromoutlet 208 to the turbocharger 300.

It is preferable for the inlet 202 to be positioned as far as possiblefrom the engine 100 and exhaust system 24, such that the coolest airpossible may be allowed to enter the inlet 202. For this reason, and toprevent the intake of snow, an inlet opening 211 (shown in FIG. 4) maybe located within an upper portion 28 of the snowmobile 10 (shown inFIGS. 1 and 4) proximate the steering control assembly 20. It iscontemplated that for the embodiment illustrated in FIG. 3, the inlet202 of the air box 200 may communicate with the inlet opening 211 with aheat-shielded duct or conduit shown in FIG. 4 at 213. The shielded duct213 allows cool atmospheric air to travel from the vent structure to theinlet 202 without gaining significant heat from the engine 100 andexhaust system 24. As shown in FIG. 4, it is preferable for a seal 215to be provided between the duct 213 and the inlet 202 to prevent airleakage therebetween. It is also contemplated, however that the air box200 may be positioned aft of the engine 100 such that the inlet 202 maydirectly communicate with the inlet opening 211 or such that arelatively shorter length of heat-shielded duct 213 may be necessary. Afilter (not shown) may be positioned at inlet 202 or the inlet opening211 within the air flow to screen or prevent particles from entering theair box 200.

As shown in FIG. 3, the turbocharger 300 communicates with the outlet208 of the air box 200 via conduit 210. Conduit 210 is preferably arigid metallic tubular member with a configuration that allows arelatively direct path from the outlet 208 to the turbocharger 300. Itis contemplated that the configuration of the conduit 210 may includeone or more bends to accommodate positioning of various engine orsnowmobile components and the relative positions of the outlet 208 andturbocharger 300. It is also contemplated that the conduit 210 may havea flexible metallic configuration or may be formed of plastic material.However, due to the heat present at the relative proximity of the engine100, it is preferable for the conduit 210 to be relatively resistant tohigh-heat environments. As shown in FIG. 3, the conduit 210 is securedat each end to the outlet 208 and the turbocharger 300 with a fasteningdevice 212.

FIG. 5 shows the fastening device 212 in more detail. As shown, thefastening device 212 may include one or more circular clamps 214 and aflexible member 216. The flexible member 216 has a configuration thatallows it to be disposed around the outlet 208 on one end and anassociated end portion of the conduit 210 on an opposite end. Thecircular clamps 214 are then secured around the flexible member 216proximate each end thereof to thereby secure the flexible member 216 toeach of the outlet 208 and the conduit 210. It is preferable for thefastening device 212 to include the flexible member 216 to allowrelative vibrational movement between each of the outlet 208, conduit210 and the turbocharger 300 to prevent fatigue stress and possiblecracking of any of these parts or the fastening device 212 itself, asmay occur with a rigid connection at these points due to vibrationscaused by the engine 100 and movement of the snowmobile 10.

Referring back to FIG. 3, the turbocharger 300 includes a compressorportion 302 and a turbine portion 304. The compressor portion 302 has aninlet 306 which is connected to conduit 210, as described above, and hasan outlet 308 that is connected to a duct or conduit 310, similarly tothe connection between the conduit 210 and the inlet 306. Turbineportion 304 includes an inlet 312 and an outlet 314. As statedpreviously, the turbocharger 300 utilizes energy provided by the exhaust(generated by the engine 100) to compress (pressurize) air from theatmosphere. FIG. 6 shows one type of turbocharger that may be used forthe intake system 22. As shown, a turbine structure 316 is connected toa compressor structure 318. For the type of turbocharger shown in FIG.6, turbine structure 316 and compressor structure 318 are integral.However, it is noted that any other type of turbocharger may be used,including types that have separate turbines and compressors that arelinked, for example by a rigid shaft that extends therebetween.

For the turbocharger shown in FIG. 6, the turbine structure 316 isconnected to compressor structure 318 so as to rotate in unisontherewith. A turbine housing 320 is configured to direct the exhaustgases from the engine onto the turbine structure 316 in a tangentialdirection to produce rapid rotational movement thereof. The exhaustgases are then expelled from the turbine portion 304 through outlet 314and flow into the exhaust system 24. As the turbine structure 316rotates, the compressor structure 318 rotates simultaneously therewith.A compressor housing 322 cooperates with the compressor structure 318 todraw air from the air box 200 into the compressor portion 302. Thecompressor structure 318 is configured to compress the air within thecompressor portion 302 and directs the pressurized air out of thecompressor outlet 308.

A waste gate, or bypass valve 324, shown in FIGS. 3 and 6, isoperatively linked to turbine housing 320. The turbine housing 320provides an alternate flow path from the turbine inlet 312 to theturbine outlet 314, while the waste gate 324 allows a predeterminedvolume of exhaust gas to bypass the turbine structure 316 from theturbine inlet 312 and discharge out of the turbine outlet 314, therebyboth reducing the pressure output of the turbine portion 302 anddecreasing the amount of back pressure between the engine 100 and theturbocharger 300. As such, the speed of the turbine structure 316 andthe amount of pressurized air being discharged from the turbine portion302 may be altered for any state of engine operation. The waste gate 324is adjustable to allow for varying amounts of exhaust to bypass theturbine structure 316 for varying performance needs of the engine.

The benefits of the use of turbocharger 300 in conjunction with theengine 100 include enhanced performance and improved efficiency. As thepressurized air exiting the compressor portion 302 is denser than theunpressurized air entering the compressor portion 302, a given volume ofthe pressurized air includes a larger quantity of oxygen than a givenvolume of the non-pressurized air. A larger volume of oxygen present inthe combustion chamber of the engine 100 upon ignition facilitatescombustion of a greater amount of fuel, thereby minimizing unburned fuelexiting with the exhaust and increasing the power output-to-fuel inputratio of the engine. However, as the turbine structure 316 is directlylinked to the compressor structure 318, the compressor structure 318induces cyclical pressurization of the air which produces a series ofhigh amplitude pressure peaks (high pressure magnitude) coinciding withthe exhaust strokes of the cylinders and a series of low amplitudepressure troughs (low pressure magnitude) coinciding with the intake,compression and power strokes of the cylinders. Therefore, the engineconfiguration (i.e. the timing of the exhaust strokes of the cylinders)determines the pressurization cycle of the air exiting the compressorportion 302. For example, during the exhaust strokes of the engine 100,a high pressure exhaust gas pulse is delivered to the turbine portion304. Consequently, the rotational velocity of the turbine structure 316is increased in proportion to the amplitude of the exhaust pulse and ahigh amplitude intake air pressure pulse is generated by the compressorportion 302. Conversely, during the remaining strokes (intake,compression and ignition) a relatively low pressure exhaust gas flow isdelivered to the turbocharger 300, producing low pressure amplitudeintake air.

Furthermore, during low speed engine operation, the exhaust strokes ofthe engine occur relatively slowly and, as such, the frequency of thehigh amplitude pressure peaks produced by the compressor portion 302 isrelatively lower. Upon rapid throttle advancement, such as at rapidtakeoff from idle or during maneuvering, the generation of highamplitude pressure peaks “lags” due to the time required for theincreased exhaust pressure (from the increased combustion rate of theengine) to spin-up (rotate synchronously with the exhaust gases from theengine 100) the turbine structure 316. Subsequently, increased air flowdemands from the engine 100 are not met by the compressor portion 302and as such, the power increase from the turbocharger 300 is notavailable. Additionally, as the turbine structure 316 may be rotatinginsufficiently to displace the increased amount of exhaust gasesproduced from the engine 100, back pressure may be produced between theengine 100 and the turbine portion 304, which may actually decrease theamount of power the engine 100 generates until the turbine structure 316spins-up. Resistance of the turbine structure 316 to spin-up is causedby the force exerted on the increased volume of air being compressed inthe compressor portion 302 and the force of suction from the resistanceof the air from the air box 200.

As shown in FIG. 3, the compressor outlet 308 communicates with theintercooler 400 by a duct or conduit 310. Conduit 310 is connected onone end to the compressor outlet 308 and is connected on an opposite endto an inlet port 401 of the intercooler by a pair of fastening devices316, similar to fastening device 216. As with conduit 210, conduit 310is preferably formed from a heat resistant material, such as metal orheat resistant plastic and is configured to provide a relatively directair path between the turbocharger 300 and the intercooler 400.

FIG. 7 shows one embodiment of the heat exchanger 400 as being locatedproximate the forward portion 26 of snowmobile 10 in a verticalposition. As stated previously, the heat exchanger 400 is constructedand arranged to dissipate heat from the pressurized air exiting theturbocharger 300. As shown in FIG. 8, the heat exchanger 400 includes anintake portion 402, which provides inlet port 401, and an outlet portion404, which provides an outlet port 405. The intake and outlet portions402, 404 are interconnected by a spaced series of elongated conduits406. As shown in FIG. 8, air from the turbocharger 300 enters throughthe inlet port 401 of intake portion 402 from conduit 310. The air isdirected through the series of conduits 406 toward the outlet port 405.It is preferable for the heat exchanger 400 to be formed of a heatconductive material such as metal, for example, aluminum or steel. Theheat conductive material of the conduits 406 allows heat from the airflowing therein to dissipate therethrough and into the atmosphere. It ispreferable for the wall thickness of the conduits 406 to be relativelythin to expedite the heat dissipation. It is also preferable for theconduits 406 to be configured so as to minimize air flow resistance andpressure loss of the air flowing therein, such as with relatively largebreadth cross-sectional geometries. It is also preferable for spaces 407between the conduits 406 to be sufficiently wide so as to allow arelatively large amount of air to pass therethrough without producingsignificant air resistance. However, it is also preferable to keep boththe cross-sectional size and distance between conduits 406 to a minimum,to maintain a space efficient design of the intercooler 400.

As shown in FIG. 7, it may be preferable for the heat exchanger to bemounted in a position that is generally normal to the movement of airproduced from forward movement of the snowmobile 10. This arrangementdirectly exposes the conduits 406 to the flow of oncoming air, which mayfacilitate heat dissipation.

It is also contemplated that the heat exchanger 400 may be mounted suchthat it is arranged parallel to the oncoming air, when the snowmobile 10is moving generally forwardly. As such, only a forward edge 408 of theintercooler 400 is exposed to the oncoming air. As illustrated in FIG.9, providing air flow over an upper side 410 of the heat exchanger 400(relative to the horizontally mounted position), such as indicated by L,produces a lower pressure relative to the upper side 410 that entrainsair from below the heat exchanger 400 through the spaces 407 to liberateheat from the conduits 406. In this arrangement, a body panel, such asindicated in FIG. 7 at 30 may be provided forward of the heat exchanger400 to protect the heat exchanger 400 from impacts with debris. Anopening 32 within the panel 30 provides air flow across the upper side410 of the heat exchanger, as prescribed above for sufficient heatdissipation. It is noted that the opening 32 may also be positioned soas to provide air flow across a lower side 412 of the heat exchanger 400thereby entraining air from the upper side 410 toward the lower side 412between the conduits 406.

It is, of course, possible to orient the heat exchanger at any positionother than parallel and normal to the flow of air. For example, FIG. 10shows the heat exchanger 400 at about a 45° angle relative to the airflow direction.

As shown in FIG. 3, the outlet port 405 of the heat exchanger 400communicates with the external plenum 500 via a conduit 414. It may bepreferable for the conduit 414 to be formed of a polymer material, sincethe temperature of the air exiting the heat exchanger 400 may berelatively lower than the air entering the heat exchanger 400. A pair ofclamps 416, similar to the clamps 214, may be used to secure respectiveends of the conduit 414 to the outlet port 405 and the plenum 500.

As shown in FIG. 3, the plenum 500 includes an inlet port 502 and anoutlet port 504. Inlet port 502 is secured to conduit 414 with the clamp416. The outlet port 504 is communicated to the engine air intake 110.It is preferable for the plenum 500 to be connected to engine air intake110 in a relatively direct manner, so as to minimize the air traveldistance between the plenum 500 and the engine 100. It is noted that theplenum 500 may be preferably formed of a metallic material. However, itis contemplated that a rigid polymer material may also be utilized. Theplenum 500 is preferably a substantially hollow enclosure, whichpossesses a relatively large volume.

As described previously, pressurized air from the turbocharger 300 has acyclical pressure pattern derived from the pulses of the exhaust gasesgenerated by the engine 100. As the frequency of the high pressure peaksof the intake air may be out of phase with the intake strokes of thecylinders, the cylinders may intake varying amounts of high density aircausing erratic performance of the engine 100. Due to the large volumeof the plenum 500, high pressure peaks entering the plenum 500 may bedissipated. Furthermore, the plenum 500 serves to bank a potential ofrelatively high pressure intake air. Due to the dissipation of the highpressure peaks and the banking of a relatively high pressure potential,the engine 100 may intake air with a relatively constant pressureamplitude.

It may be preferable for the plenum 500 to possess a volume of betweenand including 3 and 5 liters. It may be especially preferable for theplenum 500 to possess a volume of 3.5 liters. It is contemplated,however that the plenum 500 may be utilized with volumes below or above3 and 5 liters. It is noted that the plenum volume may be altered withrespect to engine size, engine operating characteristics, and/orturbocharger output.

The illustrated embodiment of the plenum 500 is directed to an elongatedrectangular structure, as shown in FIG. 3. It is contemplated, howeverthat any of various configurations may be utilized to perform anequivalent function. For example, a duct, hose or pipe member with arelatively large diameter (or breadth, in the case of non-circularconfigurations) may be utilized.

As further illustrated in FIG. 3, the engine 100 communicates with theplenum 500 at the air intake 110. The air intake 110 is preferablyprovided by a throttle body 112, which regulates an amount of air thatenters the engine 100 corresponding to throttle position.

The engine shown in FIG. 3 has a V-twin configuration, which includesthe cylinders 102, 104 that are angularly opposed to each other. It iscontemplated that the angle between the cylinders 102, 104 may bebetween 180° and 0°. However, it is preferable for the angle between thecylinders 102, 104 to be between 90° and 60°. It may be especiallypreferable for the angle to be about 80°. It is contemplated that anangle between the cylinders 102, 104 less than 80° may require abalancer, such as a harmonic balancer, to counteract and oppose thepower strokes of the cylinders 102, 104 to prevent excessive vibrationof the engine 100. For this reason, it may be advantageous for theengine 100 to include the 80° angle between the cylinders 102, 104 tolower the vibrations produced by the engine and forego the balancer. TheV-twin engine has the associated cylinder heads 106, 108 secured to anupper portion of each cylinder 102, 104. Each cylinder head 106, 108 hasa respective plurality of valves (not shown) which includes one or moreintake valves and one or more exhaust valves (not shown), each of whichcommunicates with their associated combustion chambers (not shown). Itis contemplated that the displacement of each cylinder 102, 104 bebetween 300 and 750 cm³ (cc), corresponding to a total enginedisplacement of between 600 and 1500 cc, respectively. It is preferablefor each cylinder 102, 104 to have a displacement of about 650 cc,corresponding to a total engine displacement of about 1300 cc. It iscontemplated, however that the engine displacement may be increased ordecreased due to power needs and/or space considerations of thesnowmobile. Therefore, the above-described displacement values are notmeant to be limiting. An integral plenum 114 provides pathways betweenthe throttle body 112 and each cylinder head 106, 108 through whichpressurized air from the plenum 500 flows to the intake valves forintake into an associated combustion chamber. Additionally, eachcylinder head 106, 108 has an exhaust outlet from which exhaust gasesmay be expelled from the respective combustion chambers through theexhaust valves. Heat-resistant piping 116, schematically illustrated inFIG. 11, is connected to each exhaust outlet and is connected to aconnecting structure 118 prior to connection to the turbine inlet 312 ofthe turbocharger 300. As such the exhaust gases from both cylinders arerouted through the turbine portion 304 of the turbocharger 300.

The above discussion of a four-stroke V-twin engine is meant only as anexample of one type of engine that may be used to power the snowmobile10 and that may be used in conjunction with the air intake system 22 ofthe present invention. It is, of course, possible to use any other typeof four-stroke engine with the intake system 22. For example, FIGS. 12and 13 schematically illustrate two and three cylinder, in-linefour-stroke engines, respectively at 700 and 800.

The two cylinder engine indicated at 700 in FIG. 12 includes a pair ofcylinders 702, 704 that are disposed generally in-line with one anotherand have pistons (not shown) housed therein, which are operativelycoupled to a common crankshaft (not shown). As with the engine 100, theengine 700 is fed pressurized air from the plenum 500 via an air inlet706, which may be provided by a throttle body or carburetor(s). Asfurther illustrated, pressurized air is supplied to each cylinder 702,704 by a plenum, or intake manifold, indicated by 708. Exhaust outlets710, 712 of each cylinder 702, 704 are connected to the inlet 312 of theturbocharger 300 via exhaust conduit 714, similar to conduit 116. Theexhaust conduit 714 includes a branched portion 716, which is connectedto the inlet 312. In this manner, the engine 700 is supplied withpressurized air from the turbocharger 300 and powers the turbocharger300 with exhaust gas from the exhaust outlets 710, 712.

The three cylinder engine indicated at 800 in FIG. 13 includes threecylinders 802, 804, and 806 that are disposed generally in-line with oneanother and have pistons (not shown) housed therein, which areoperatively coupled to a common crankshaft (not shown). As with theengines 100 and 700, the engine 800 is fed pressurized air from theplenum 500 via an air inlet 808, which may be provided by a throttlebody or carburetor(s). As further illustrated, pressurized air issupplied to each cylinder 802, 804, and 806 by a plenum, or intakemanifold, indicated by 810. Exhaust outlets 812, 814, and 816 of eachcylinder 802, 804, and 806 are connected to the inlet 312 of theturbocharger 300 via exhaust conduit 818, similar to conduits 116 and714. The exhaust conduit 818 includes a branched portion 820, which isconnected to the inlet 312. In this manner, the engine 800 is suppliedwith pressurized air from the turbocharger 300 and powers theturbocharger 300 with exhaust gas from the exhaust outlets 812, 814, and816.

For the V-twin engine discussed above, exhaust gas flowing from theengine 100 is pulsed (i.e. has a cyclical pressure peak frequency) dueto the firing sequence of the cylinders 102, 104. With the configurationof the cylinders 102, 104 of the V-twin engine 100, the firing sequenceincludes the rapid successive ignition of each cylinder 102, 104.Therefore, the exhaust strokes of the cylinders 102, 104 occurrelatively close together. This arrangement produces a pair of highamplitude exhaust pressure peaks derived from the exhaust strokes ofeach cylinder 102, 104 followed by low amplitude exhaust pressure duringthe three remaining strokes (intake, compression and power strokes) ofeach cylinder. In other words, the exhaust pressure signature includes apair of high pressure pulses with a lull of low exhaust pressurein-between successive exhaust strokes. As described hereinabove,consequent to the pulsed nature of the exhaust gas flow, the pressurizedair generated by the turbocharger 300 will also possess a pulsed flow.For this reason, the plenum 500 is advantageous to provide intake airfor the engine 100 with a relatively constant high pressure.

For the in-line type engines 700, 800 (FIGS. 12 and 13, respectively),exhaust gas flowing from the engine 100 is pulsed (i.e. has a cyclicalpressure peak frequency) due to the firing sequence of the cylinders.Consequently, the pressurized air generated by the turbocharger 300 willpossess a pulsed flow corresponding to the ignition sequence of therespective engine. As with the V-twin engine discussed above, the plenum500 is advantageous to provide intake air for the respective engine at arelatively constant high pressure.

Selection of a particular type of engine discussed herein may be basedon space limitations within the snowmobile 10. FIG. 14 is a plan view ofthe V-twin engine 100, two cylinder engine 700, and three cylinderengine 800. Depending on the specific power requirements and spacelimitations of a snowmobile 10, any one of these engines may be utilizedwith the snowmobile. As shown, the width of the two and three cylinderengines 700, 800 is relatively narrower than that of the V-twin engine100. However, the length of the V-twin engine 100 is relatively lessthan either of the two or three cylinder engines 700, 800.

It is noted that the present invention is advantageous in the art ofsnowmobiles for providing a powerful four-stroke engine that producesrelatively fewer hydrocarbon emissions than the prior two-strokecounterparts. It is also noted that due to the previouslydisadvantageous characteristics of four-stroke engines, with respect toimplementation thereof with snowmobiles, the present invention has beenunpracticed in the art.

Furthermore, with respect to the turbocharger 300, previous use of aturbocharger has been unfeasible in a snowmobile due to turbo lag,described above, during rapid throttle advancement. Consequent to thenature of snowmobiles and the environment they are operated in, rapidthrottle advancement is a common occurrence in normal and severeoperating conditions. This can result in turbo lag in a turbochargedengine. However, the use of a continuously-variable-transmission (CVT)in the snowmobile, as is well known in the art, can help reduce orprevent turbo lag. For example, it is noted that the turbocharger 300may deliver pressurized air to the engine 100 for engine speeds below3000 RPM, and at 3000 RPM, pressurizes intake air at an effective anduseable level. The CVT may be configured to delay driving engagementuntil about 3000 RPM, therefore, the turbocharger is already effectivelypressurizing the engine by the time the CVT begins driving engagement.Thus this relatively high engine RPM prior to driving engagement of theCVT helps to minimize turbo lag. No turbo lag has been noticed in asnowmobile tested with the turbocharged engine as described herein. FIG.15, schematically shows a CVT 900 operatively connected to a crankshaft902 of an engine 904. It is noted that engine 904 may be of any typediscussed herein, such as the V-twin type, two cylinder type, of threecylinder type. Of course, it is contemplated that different enginesizes, turbocharger configurations, snowmobile sizes, and CVTconfigurations may be suited for higher or lower RPM at which point thesnowmobile initially moves. It is noted that 3000 RPM is recited forexample only and is not meant to be limiting.

Additionally, the CVT, engine, and turbocharger (as well as any othercomponents discussed herein) may be arranged so as to maximize availablespace within the snowmobile 10. For example, FIG. 15 shows the CVT 900disposed on a side of the engine 904 opposite the turbocharger 300.Conversely, FIG. 16 shows the CVT 900 disposed on a side of the engine904 adjacent the turbocharger 300. Any other accommodating arrangementis, of course, possible. Additionally, FIG. 15 shows an engine airintake, indicated at 906, arranged at the side of the engine 904adjacent the CVT 900 and opposite the turbocharger 300. Conversely, FIG.16 shows the engine air intake 906 arranged at the side of the engine904 opposite the turbocharger 300, while the CVT 900 is disposedadjacent the turbocharger 300 and opposite the intake 906. Specifically,FIG. 15 shows the CVT 900 and intake 906 disposed on a port side of theengine 904, while the turbocharger 300 is disposed on a starboard sideof the engine 904. Furthermore, FIG. 16 shows the CVT 900 andturbocharger 300 disposed on the starboard side of the engine 904, whilethe intake is disposed on the port side of the engine 904. Similarly,the plenum 500 maybe disposed on either side of the engine 904.Furthermore, although the turbocharger is shown on the air inlet side ofthe engine in FIGS. 15 and 16, it should be appreciated that theturbocharger may be provided on the exhaust outlet side of the engine.In addition, the turbocharger may be positioned on either the port orstarboard side of the engine.

As shown in FIG. 3, the turbine outlet 314 is connected to the exhaustsystem 24. The exhaust system 24 preferably includes heat-resistantpiping and a muffler (shown in FIG. 2 at 300A) through which exhaustgases from the engine exit the snowmobile 10, via the turbocharger 300.

It will be appreciated that numerous modifications to and departuresfrom the embodiments of the invention described above will occur tothose having skill in the art. Such further embodiments are deemed to bewithin the scope of the following claims.

1. A snowmobile, comprising: a frame having a forward portion and a rearportion; a turbocharged four-stroke engine mounted to said forwardportion of said frame; an endless belt drive system mounted to said rearportion of said frame and operatively connected to said engine; an airintake system for said engine; and a continuously-variable-transmissionoperatively coupled between said engine and said belt drive system andbeing manipulable into an engaged configuration wherein saidcontinuously-variable-transmission transfers sufficient power betweensaid engine and said endless drive belt to effect movement of saidsnowmobile.
 2. A snowmobile as in claim 1, wherein said engine includesat least one cylinder, each cylinder having a respective combustionchamber, said engine having an air inlet capable of communicating witheach said combustion chamber and an exhaust outlet capable ofcommunicating with each said combustion chambers; said air intake systemcomprising; an air passage communicated with the atmosphere, said airpassage being a substantially hollow enclosed structure, wherein saidturbocharger is connected to said air passage such that air from saidair passage may enter said turbocharger, said turbocharger communicatingwith said exhaust outlet and being constructed and arranged such that aflow of exhaust gases from said exhaust outlet through said turbochargeraffects a pressurization of air therein.
 3. A snowmobile as in claim 2,further comprising a heat exchanger formed of a heat conductive materialconnected to said turbocharger such that the pressurized air from saidturbocharger may enter therein, said heat exchanger being constructedand arranged such that heat from the pressurized air is dissipatedtherefrom to the atmosphere via said heat conductive material.
 4. Asnowmobile as in claim 3, further comprising a plenum connected to saidheat exchanger such that air from said heat exchanger may enter saidplenum, said plenum further connected to said air inlet and beingconstructed and arranged such that cyclically pressurized amplitude ofthe air from said turbocharger via said heat exchanger may collecttherein such that the pressurization amplitude of the air upon exitingthe plenum and entering said air inlet is substantially constant.
 5. Asnowmobile as in claim 2, wherein said air passage is positioned forwardof said engine in spaced relation thereto in order to preventsignificant heating of air within said air passage.
 6. A snowmobile asin claim 2, wherein said air passage is positioned aft of said engine inspaced relation thereto in order to prevent significant heating of airwithin said air passage.
 7. A snowmobile as in claim 3, wherein saidheat exchanger is an intercooler, said intercooler inducing an intakeportion and an outlet portion, said intake and outlet portions connectedby a series of spaced hollow conduits.
 8. A snowmobile as in claim 7,wherein said intercooler is positioned proximate said forward portion ofsaid frame, said intercooler being arranged generally normally to theoncoming air flow from the atmosphere produced by movement of saidsnowmobile therethrough, such that said conduits are directly exposed tothe oncoming air.
 9. A snowmobile as in claim 7, wherein saidintercooler is positioned proximate said forward portion of said frame,said intercooler being arranged generally parallel to the oncoming airflow from the atmosphere produced by movement of said snowmobiletherethrough, said intercooler being positioned such that the air isdirected across one surface thereof, thereby entraining air from anopposite side through spaces between said conduits.
 10. A snowmobile asin claim 7, wherein said intercooler is positioned proximate saidforward portion of said frame, said intercooler being arranged at anangle to the oncoming air flow from the atmosphere produced by movementof said snowmobile therethrough, said intercooler being positioned suchthat the air is directed across one surface thereof, thereby entrainingair from an opposite side through spaces between said conduits.
 11. Asnowmobile as in claim 3, wherein said air passage communicates withsaid turbocharger via a first duct member and said turbochargercommunicates with said heat exchanger via a second duct member.
 12. Asnowmobile as in claim 4, wherein said heat exchanger communicates withsaid plenum via a duct member, said duct member being formed of one of apolymer material and a metallic material.
 13. A snowmobile as in claim4, wherein said plenum is connected to said air inlet on one endthereof.
 14. A snowmobile as in claim 4, wherein said plenum has aninternal volume between and including 3 and 5 liters.
 15. A snowmobileas in claim 2, wherein said snowmobile further comprises un exhaustsystem, said exhaust system being operatively connected to saidturbocharger such that exhaust gas may flow from said turbochargersubsequent to said affecting the pressurization of air from theenvironment and through said exhaust system into the atmosphere.
 16. Asnowmobile as in claim 15, wherein said exhaust system includes amuffler to dissipate noise of the exhaust gas exiting said engine.
 17. Asnowmobile as in claim 2, wherein said air inlet is provided by athrottle body.
 18. A snowmobile as in claim 2, wherein said turbochargerpressurizes the air at a sufficiently useable level for engine speedsbelow 3000 revolutions per minute.
 19. A snowmobile as in claim 1,wherein said continuously-variable-transmission is operatively connectedto said engine on a side thereof opposite a side thereof that isproximate said turbocharger.
 20. A snowmobile as in claim 1, whereinsaid continuously-variable-transmission is operatively connected to saidengine on a side thereof adjacent a side thereof that is proximate saidturbocharger.
 21. A snowmobile as in claim 1, wherein saidcontinuously-variable-transmission is configured such that the movementof said snowmobile is effected when said engine is operating at 3000revolutions per minute.
 22. A snowmobile as in claim 1, wherein saidturbocharger pressurizes the air prior to engagement of saidcontinuously-variable-transmission.
 23. A snowmobile as in claim 1,wherein said engine is of a V-twin two cylinder type engine.
 24. Asnowmobile as in claim 1, wherein said engine includes a plurality ofcylinders and is an in-line type engine.
 25. A snowmobile as in claim 1,wherein said turbocharger is disposed on a starboard side of saidengine.
 26. A snowmobile as in claim 1, wherein said turbocharger isdisposed on a port side of said engine.
 27. A snowmobile as in claim 4,wherein said plenum and said continuously-variable-transmission aredisposed on a same side of said engine.
 28. A snowmobile as in claim 4,wherein said plenum and said continuously-variable-transmission aredisposed on opposites sides of said engine relative to one another. 29.A snowmobile as in claim 4, wherein said plenum and said turbochargerare disposed on opposite sides of said engine relative to one another.